django-vcexport 0.6

a flexible library for exporting serialized django model instances to a version-controlled repository automatically or manually

How it works

There is an application-level API and a model-level API.

Use the model-level API to define export behavior per model class, with automatic exports on save.

Use the application-level API to define export behavior in views (for example) and explicitly trigger content export from your own code.

The model-level API

The design is inspired by Django’s ModelAdmin and ModelForm aspect-oriented pattern. The core behaviors are defined in the vcexport.models.Exporter class, which is analogous to ModelAdmin. Like ModelAdmin and ModelForm, you will subclass the default base to customize the behavior on a per-model basis.

1. For automatic versioning of models, register them with vcexport:

   import vcexport
   vcexport.register(MyModel)

   This will connect a post_save signal.

2. You can customize the export behavior on a per-model basis by subclassing vcexport.models.Exporter and telling vcexport to register your model with the custom Exporter:

   class MyExporter(vcexport.models.Exporter):
     ...
   vcexport.register(MyModel, exporter=MyExporter)

3. By default, models are serialized to django’s XML format, because it works well with diff and is generic.

4. You can customize the serialization per model by passing a custom template path as a class attribute:

   class MyExporter(Exporter):
       repository_template = 'fleem/document_format.txt'

   The template will be rendered with two context variables; object which is the model instance that was saved, and a boolean created:

   {% if created %}New object!{% endif %}
   {{object.title}}
   {{object.related_field.pk}}
     ****
   Color: {{object.color}}
   {{object.description}}

   This allows alternate use cases to be supported:

   • You want to version a model wholesale

   • You have a model which has one or two document-like text fields, and you want to version those fields only – just don’t write out any other fields in the serialization template.

5. By default the document dumps of your model instances will be saved in repository paths that look like /app_name/ModelClassName/instance_pk.

   You can customize the path:

   class MyExporter(Exporter):
       def repository_path(self):
           return '/my_custom/path_for/this_model/' + self.object.color

   Note that if you do this, you may end up with multiple model instances that save to the same file path in the repository. This is a feature.

6. The default committing user is undefined. At present you cannot customize this.

   The default commit message is uninteresting: “Object {{instance.pk}} (from ‘{{app_name}}.{{model_name}}’) saved by django-vcexport.”

   You can customize the commit message with a model method that takes a boolean created, and returns a string:

   class MyExporter(Exporter):
       def repository_commit_message(self, created):
           if created:
               return "User %s committed a new %s" % (
                 self.object.user.username, self.object.color)
           return "User %s committed %s" % (self.object.user.username,
                                            self.object.color)

The application-level API

You can also export the content explicitly, for example in your model’s save() method, in view code, etc, with the vcexport.export_to_repository function:

def my_view(request):
    ...
    object = MyModel.objects.get(...)
    object.morx = request.POST['new_morx']
    object.save()

    import vcexport
    vcexport.export_to_repository(object)

The default template, commit message, etc are the same as with the model API. You can customize them in your own code and pass them to export_to_repository:

def my_view(request):
    ...
    object, created = MyModel.objects.get_or_create(...)
    object.morx = request.POST['new_morx']
    object.save()

    import vcexport
    vcexport.export_to_repository(
               object, created=created,
               repository_template='fleem/morx.html',
               message="Changed the morx",
               repository_path='/fleem/objects/%s' % object.pk)

The export_to_repository function will return the Revision of the commit, or None if there were no changes to commit.

A middle ground

You may want both the organizational benefits of grouping your behavioral definitions into an Exporter, and the flexibility of triggering exports explicitly in your application code.

You can invoke an Exporter instance directly to satisfy this yen:

def my_view(request):
    ...
    object, created = MyModel.objects.get_or_create(...)
    object.morx = request.POST['new_morx']
    object.save()

    exporter = MyExporterSubclass(object)

    exporter.export_to_repository(object, created=created)

Like vcexport.export_to_repository this will return the Revision of the commit or None if the operation resulted in no committed changes.

If you want to do this, you will likely not want to register the same models for automatic post_save export – but maybe you do!

Configuration

You must provide one piece of configuration in your settings.py file:

• VCEXPORT_CHECKOUT_DIR: the absolute path to a local checkout of the repository that you want to store your data in

You may provide additional settings.py configuration:

• VCEXPORT_BACKEND: one of ‘svn’ or ‘bzr’

To use with Subversion, you must have pysvn installed.

To use with Bazaar, you must have bazaar installed.

If this setting is not specified, the default is Subversion; however, Bazaar is really a better backend in a lot of ways (including speed for synchronous commits) and will likely become the primary supported backend in the future.

You will have to initialize your repository // checkout on your own.

Credits

Originally developed at Columbia University’s Center for New Media Teaching & Learning <http://ccnmtl.columbia.edu>

The source code is available on github <http://github.com/ejucovy/django-vcexport>

New in this version

• Made Exporter importable as vcexport.Exporter

• Removed ‘hg’ option for VCEXPORT_BACKEND, since sven no longer supports this.

• Added new ‘bzr’ option for VCEXPORT_BACKEND.

History

0.5.1 (06-12-09)

Brown-bag release; made export_to_repository function available as public API (vcexport.export_to_repository)

0.5 (06-12-09)

Split apart distinct APIs for model-level behavior and application-level usage.

0.4 (24-11-09)

Initial release. This package was previously called svndjango. It was redesigned from the ground up and renamed django-vcexport to describe more accurately what it does.